The invention relates to an apparatus for devices for determining properties of applied layers.
When coating substrates, for example optical lenses and glasses, it is important to acquire the properties of the applied layers, for example in order to be able to determine the time at which the coating is to be terminated. In particular multiple coatings, which are employed in the production of high-quality optical objects such as beam splitters, color conversion filters, cold light mirrors and laser mirrors, require highly precise measuring devices to ensure the quality and the reproducibility of the coatings. The physical properties which define the quality of thin layers are essentially the transmission, reflection, absorption, scattering, thermal stability and moisture resistance as well as the abrasion resistance and adhesiveness.
For determining the thickness and measuring the coating rate, i.e. of the mass applied per unit time, crystal oscillators are already known, whose crystal is coated in a manner similar to the substrate (DE 31 20 443 C2). Its mass is changed through the coating of the crystal, which, in turn, has an effect on the frequency of the crystal oscillator. The frequency change of the crystal oscillator is consequently a measure of the thickness of the deposited layer, while the frequency change per unit time can serve as a measure of the coating rate.
While the coating rate can be determined relatively precisely by means of a crystal oscillator, the measurement of the absolute layer thickness entails imprecisions such that for this purpose other measuring methods, for example optical ones, are preferred. In the case of optical measuring methods the applied thin layer is irradiated with a light beam and the reflected beam is compared with the irradiating beam. Based on the ratio of irradiating to emitted light beam it is possible inter alia to determine the thickness of the layer.
Thus, for measuring the transmission of an [epitaxially] grown layer on a test glass a spectral photometer is utilized (DE 43 14 251 A1) during the coating. The white light of a halogen lamp is conducted with a light waveguide to a vacuum lead-through with imaging optics and through the imaging optics imaged onto the test glass. A second vacuum lead-through with imaging optics images the transmitted light on a monochrometer or a line filter with succeeding detector.
It is also known to determine the growth of layers optically with the aid of a light source with detector and a test glass as well as also with the aid of crystal resonators (DE 37 42 204 A1).
It is further known that a light source emits a light beam with specific wavelength onto a film thickness control substrate, which is reflected onto a detector (DE 693 09 505 T2, corresponding to EP 0 552 648 B1). The quantity of light reflected from a film thickness control substrate varies as a function of the index of refraction and thickness of the thin film which has formed on the film thickness control substrate.
The invention addresses the problem of providing an apparatus with which the determination of the properties of a layer by means of a crystal oscillator and an additional optical method is carried out.
This problem is solved according to the present invention.
The invention consequently relates to an apparatus for devices for determining properties of thin layers, which are applied onto substrates. This apparatus comprises two changing magazines with one magazine being provided for crystal resonators and the other for test glasses. The changing magazine for crystal resonators has the form of a disk and is encompassed by the annular magazine for test glasses. Both can be rotated independently of one another. With the aid of sensors and evaluation devices each position of the magazines can be reproduced. Therewith it is possible to carry out multiple coatings.
One advantage attained with the invention comprises that it can be applied with an online process regulation or with the precise determination of switch-off conditions during the epitaxial growth of thin layers in order to measure the reflection or transmission on test glasses or on the substrate itself.
A further advantage of the invention comprises that several test glasses and several crystal resonators can be provided and be brought into specific positions. Furthermore is of advantage that the test glasses and the crystal resonators can readily be exchanged. If a test glass ring is utilized instead of several individual test glasses, the different positions of this test glass ring can be encountered reproducibly and repeatedly.
An embodiment example of the invention is shown in the drawing and will be described in further detail.